This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To test the validity of our primary HIV-1 infection model using a non-human primate model for HIV-1/AIDS. To examine evolution of the viral nef genes from a single transmitted strain during the acute phase of SIV infection, we sequenced full-length nef genes longitudinally using the method of single genome amplification. The acute phase of immunodeficiency virus infection plays a crucial role in determining steady-state virus load and subsequent progression of disease in both humans and nonhuman primates. Recently we developed a Monte-Carlo simulation with mathematical analysis of viral evolution during primary HIV-1 infection that enables classification of new HIV-1 infections originating from multiple versus single transmitted viral strains and the estimation of time elapsed following infection. Results: A total of 207 SIV nef SIV sequences, collected during the first 3 weeks following experimental infection of two rhesus macaques with the SIVmac239 clone, were analyzed and found to display a comparable level of genetic diversity, 0% to 0.053%, with that of env sequences from acute HIV-1 infection, 0.005% to 0.127%. We confirmed that the acute HIV-1 infection model correctly identified the experimental SIV infections in rhesus macaques as "homogenous" infections, initiated by a single founder strain. The consensus sequence of the sampled strains corresponded to the transmitted sequence as the model predicted. However, measured sequential decrease in diversity at day 7, 11, and 18 post infection violated the model assumption, neutral evolution without any selection. While nef gene evolution over the first 3 weeks of SIV infection originating from a single transmitted strain showed a comparable rate of sequence evolution to that observed during acute HIV-1 infection, a purifying selection for the founder nef gene was observed during the early phase of experimental infection of a nonhuman primate. This research used WNPRC Immulogy &Virology and Genetics Services.